Recently, a light emitting diode (LED) is spotlighted as a light emitting device. Since the LED can convert electric energy into light energy with high efficiency and long life span of about 5 years or more, the LED can remarkably reduce the energy consumption and repair and maintenance cost. In this regard, the LED is spotlighted in the next-generation lighting field.
Such an LED includes a buffer layer formed on a growth substrate having a hexagonal crystal system, such as a sapphire substrate, a silicon carbide (SiC) substrate or a silicon (Si) substrate. In addition, a light emitting semiconductor layer including a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer is formed on the buffer layer. The LED may include a group III nitride epitaxial semiconductor and the active layer may emit light as current is applied thereto through the first and second conductive semiconductor layers.
However, if the group III nitride epitaxial semiconductor is formed on the growth substrate, the crack or warpage may occur in the group III nitride epitaxial semiconductor and the dislocation is generated due to the difference in lattice constant and thermal expansion coefficient between the group III nitride epitaxial semiconductor and the growth substrate.
In particular, if the group III nitride epitaxial semiconductor is grown on a silicon growth substrate, the crystal property of the group III nitride epitaxial semiconductor may be degraded and the crack and the dislocation may occur due to the great difference in lattice constant and thermal expansion coefficient between the group III nitride epitaxial semiconductor and the silicon growth substrate.
For example, nitride gallium (GaN), which is the representative group III nitride epitaxial semiconductor, has the thermal expansion coefficient of 5.59×106/K and the lattice constant of 3.189 Å. In contrast, the silicon growth substrate having the crystal plane [111] has the thermal expansion coefficient of 2.50×106/K and the lattice constant of 3.84 Å.
That is, the silicon growth substrate has the difference in thermal expansion coefficient of about 53.6% and lattice constant of about 16.9% when comparing with the nitride gallium (GaN). Thus, the great dislocation may occur in the GaN layer grown on the silicon growth substrate due to the difference in lattice constant and the crack may occur in the GaN layer due to the difference in thermal expansion coefficient.
In particular, when the GaN layer grown under the high temperature is cooled, the tensile stress is applied to the GaN layer due to the difference in thermal expansion coefficient, so that the crack may occur in the GaN layer. The crack may deteriorate the crystal property of the GaN layer and may interfere with electrons or holes being injected, thereby degrading the performance of the LED.